Heat-sensitive copy-sheet



April 3, 1962 R. OWEN 3,028,255

HEAT-SENSITIVE COPY-SHEET Filed 001'. 26, 1959 HEAFJEAIJITII/E COPY- PA PEI? INCLUDING ORGAN/C AMTNE MOLYQDATE AND RIDUC/N AGfNT THl-REFOR BACK/N6 NVENTOR Pro/A20 OWEN W,W,M {W

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3,028,255 HEAT-SENSITIVE COPY-SHEET Richard Gwen, Brooklyn Center, Minn, assignor to Minnesota Mining and Manufacturing Company, St. Paul,

' nite Bee solution. To the solution thus formed is next added a solution of one-half mol of sodium molybdate, with stirring. The resulting precipitate is removed by filtration, washed to remove sodium chloride, and dried. If desired Minn, a corporation of Delaware a further portion may be recovered by evaporation and Filed Get. 26, 1959, 581- NO- 3 3, crystallization. The product is moderately soluble in 11 Claimswater. When heated it does not melt, but decomposes 'This. application is a continuation-in-part of my 00- and converts from a white to a light brown and then to pending. application'Serial No. 594,540, filed June 28, a gray or greenish-gray color between about l85240 C. 1956 now Patent No 2,910,371 Ten grams of the tetradecyl amine molybdate product This invention relates to heat-sensitive copy-paper useis intimately dispersed in acetone y Prolonged ball ful in the thermographic reproduction of differentially ramillingp y, ten grams of ethyl cellulose and 5 diation-absorptive graphic originals as described in Miller 8 81115 of hydl'oqhihohe are dissolved in 85 grams of United States Patent No. 2,740,896 and employing appatone The tWO compositions are mixed together and ratus such as described in Miller United States Patent the mixture coated on p 0Veflay tracing P p and No. 2,740,895 or in Kuhrmeyer et al. United States Patdried- The resulting heateehsitive py-P p is White ent No. 2,891,165. In particular, the invention relates to in pp a converting to a reddish brown color when thermographic heat-sensitive copy-paper in which the reheated 111 the h g l copying PTOeeSS 0h quired visible change results from inter-reaction involv- 'y Contact Wlth a metal test bar at a temperature ing, for example, such inter-reactants as organic amine of molybdates and organic reducing agents. In a preferred The two eomposltiohs may alternatively be p l' y form the invention provides white copy-sheets, which ap With lhtermediate y The reactants are when suitably heated, as in the thermographic copying t mately associated at the interface between the conprocess, yield images in a variety of colors depending on tlguous l g The Sheet Produces Visible but some" the specific components employed A non fading copy i what less d1st1nct copy than is obtainable with singlethus directly produced, Without any Subsequent processing layer coatlngs, but pie-reaction of the reactants is avoided. such as developing, fixing, washing, treatment with Example 2 fumes p or ny other treatment Approximately equal weights of hydroquinone and A Particularly useful form 0f heat-Sensitive PY- ethylamine molybdate are mixed together in acetone, the illustrated in the pp drawing, has a visibly heathydroquinone being added to a previously prepared slur- SeIlSltlVe coating bonded to a t transparent Cartier ry of the ethylamine molybdate formed by ball milling. A further Opaque Preteetlve layer y he pplled The mixture is coated on porous paper in the absence of over the heat-sensitive layer. Heat-converted image areas a binder, and d i at room temperature, Th i i i ll within the heat-sensitive coating are then viewed through hi Sheet i Converted to a yellow color h locally the transparent P p Or other A t heated in the thermographic copying process or'by brie binder is normally used with the reactive color-forming Contact i h h mata] t t b t b t 100 C, eempenehts in the h ve layer. The binder may The addition of minor proportions of resinous 01 itself form t Camel the reactants y e P- polymeric binders to the mixture in acetone permits the ported within a fibrous web structure in the substantial abformation f fi ly bonded heap e jti coatings on f e f film-forming blhdel The reactants are main" 40 porous films and on dense papers, and increases the temtalned in the required intimate association in physically perature t hi h th color change occurs, Fo l distinct relationship and in condition for inter-reaction th dditi t th i t of E l 2 of ll m unts when briefly heated t0 ppf p conversion of ethyl cellulose produces a composition which may be perature The PY- 1S Sultable making direct, coated on non-porous paper and dried to provide a firmly high contrast, clear detail, permanent copies of typebonded heat-sensitive layer which undergoes permanent written, printed, and other graphic subject-matter. The change in color on brief contact with the test bar at about copy-sheet does not adhere to nor deface the graphic 110-120 C. original or the thermoprinting apparatus. It is stable at Polystyrene is another resinous binder material useful normal room and storage temperatures. in the practice of the invention, and coatings prepared The following examples will further illustrate but not w1th this binder are somewhat more water-resistant than limit the invention otherwise similar coatings having an ethyl cellulose binder. Example 1 Polystyrene is conveniently applied from solution in ethyl acetate or in a mixture of acetone and heptanen Other T a yl aIhlIle y t first Rrepared a binders in other solvents are also useful, and are preferlows: Tetradecyl ammo is first dissolved in an equlmolar bl so l d as to id an inert hid f h amount of Cl i aqueous Solution, with addition of alreactants in which one or both of the latter are insoluble. cohol and gentle warming where required for complete The following tabulation sets forth additional specific Example Reactant A Reaetant B Tergp Initial Final 3317;331:133: liffiri filfifi fi.ffillliiii: Ealisi'na'rnnnnin? 33 .ll iiiiiii 33312:

2, fi-dihydroxytolueue). brown. 5 cyclohexylamine molydate. hydroquinone 130 tan orangebrown. 6 hexamethylcne dlamine do white purple- 7 teti adzcyl ininemolydbate- 4 methoxy 1 hydroxy- 110 do. h3g3:

dihydronaphthalene. 8 "do; 2,4-dibromonaphthol ;do blue. 9 do catecholacetone condensa- 70 d0 browntion polymer. black. 10 pheny1aminemo1ybdate.. hydroquinone paleuow black.

components and combinations which are found useful in the practice of the invention, together with the color change produced and a typical test temperature for color conversion as determined with the heated metal test bar.

The organic amine molybdate is conveniently prepared by the procedure outlined in Example 1, viz. by reaction in aqueous solution of the amine hydrochloride with the stoichiometric quantity of sodium molybdate. Where the product is readily water-soluble, smaller quantities of water are required and suitable precautions must be observed in purifying the material.

The organic amine molybdates are themselves capable of color conversion on heating, at least in some instances. For example, tetradecyl amine molybdate as prepared in Example 1 and coated on filter-paper converts from White to greenish brown when the coated paper is briefly placed in contact with a test bar at 190200 C.; but corresponding temperatures are likely to cause charring of the paper, and are difiicult to attain, in the thermographic copying process. Phenylamine molybdate likewise, when spread in a thin layer on a supporting film or foil and heated slowly to 180-200 C., first converts to a pale green and then to black. Again, certain higher molecular weight organic components tend to increase the temperature requirements unduly; for example a heat-sensitive composition prepared with hydroquinone andoctadecyl amine molybdate converts from off-white to blue, but at a test bar temperature well above 150 C. It has previously been found that papers which provide a color change on the test bar at temperatures within the approximate range of 90-450 C., and preferably below about 120 C., are best capable of serving as thermographic copy-papers in commercially available copying apparatus. The present invention makes possible the development of a visible change in the organic amine molybdate composition at a temperature Well below the level otherwise required, and well within the range found to be essential for contemporary commercial ther'inographic copying procedures and apparatus. However the compositions requiring the higher temperatures are useful in sheets, coatings or other structure designed for printing with heated type, or for tracing with a heated stylus, or in other applications requiring a visible change on application of high temperatures.

Molybdates of other organic amines, as well as organic amine tungstates and vanadates, having equivalent properties and characteristics and useful in providing visibly heat-sensitive copying-sheets are contemplated as coming within the ambit of this invention. Other equivalent active reducing agents are likewise contemplated.

What is claimed is as follows:

1. A normally stable heat-sensitive copy-sheet suitable for the thermographic reproduction of differentially radiation-absorptive graphic originals and including a visibly heat-sensitive layer capable of undergoing pennanent visible change on brief contact of said copy-sheet with a metal test bar at a temperature within the approximate range of 70 C. to 150 C. and comprising an organic amine molybdate and a reducing agent reactive therewith.

2. A normally stable heat-sensitive copy-sheet suitable for the thermographic reproduction of diiferentially radiation-absorptive graphic originals and including a visibly heat-sensitive layer capable of undergoing permanent visible change on brief contact of said copy-sheet with a metal test bar at a temperature within the approximate range of 70 C. to 150 C. and comprising an organic amine molybdate and an aromatic hydroxy reducing agent.

3. A normally stable heat-sensitive copy-sheet suitable for the thermographic reproduction of differentially ra diation-absorptive graphic originals and including a visibly heat-sensitive layer capable of undergoing permanent visible change on brief contact of said copy-sheet with a metal test bar at a temperature within the approximate range of C. to C. and comprising an aliphatic amine molybdate and an aromatic hydroxy reducing agent.

4. A normally stable heat-sensitive copy-sheet suitable for the thermographic reproduction of differentially radiation-absorptive graphic originals and including a visibly heat-sensitive layer capable of undergoing permanent visible change on brief contact of said copy-sheet with a metal test bar at a temperature within the approximate range of 70 C. to 150 C. and comprising an aromatic amine molybdate and an aromatic hydroxy reducing agent.

5. A normally stable heat-sensitive copy-sheet suitable for the thermographic reproduction of differentially radiation-absorptive graphic originals and including a visibly heat-sensitive layer capable of undergoing permanent visible change on brief contact of said copy-sheet with a metal test bar at a temperature within the approximate range of 70 C to 150 C. and comprising an aliphatic amine molybdate and a hydroquinone.

6. A normally stable heat-sensitive copy-sheet suitable for the thermographic reproduction of differentially radiation-absorptive graphic originals and including a visibly heat-sensitive layer capable of undergoing permanent visible change on brief contact of said copy-sheet with a metal test bar at a temperature within the approximate range of 70 C. to 150 C. and comprising an aromatic amine molybdate and a hydroquinone.

7. A normally stable heat-sensitive copy-sheet suitable for the thermographic reproduction of differentially radiation-absorptive graphic originals and including a visibly heat-sensitive layer comprising tetradecylamine molybdate and hydroquinone.

8. A high temperature indicator device capable of undergoing permanent visible change when briefly heated to a conversion temperature within the approximate range of 70 C. to 240 C. and including a visibly heatsensitive layer comprising an organic amine molybdate.

9. A normally stable heat-sensitive thermographic copy-sheet capable of undergoinng permanent visible change on brief contact with a metal test bar at a temperature within the approximate range of 70 C. to 150 C. and including a layer of reactants maintained in physically distinct relationship and in condition for interreaction when thus heated, said reactants comprising a visibly heat-sensitive organic amine molybdate and an aromatic hydroxy reducing agent.

10. A normally stable heatsensitive thermographic copy-sheet capable of undergoing permanent visible change on brief contact with a metal test bar at a temperature within the approximate range of 70 C. to 150 C., said copy-sheet comprising a thin supporting web and a visibly heat-sensitive coating of a composition comprising a film-forming binder, a visibly heat-sensitive organic amine molybdate, and an aromatic hydroxy reducing agent.

11. A normally stable heat-sensitive therrnographic copy-sheet capable of undergoing permanent visible change on brief contact with a metal test bar at a temperature within the approximate range of 70 C. to 150 C., said copy-sheet comprising a thin supporting web and a visibly heat-sensitive coating of a composition comprising a film-forming binder, tetradecylamine molybdate, and an aromatic hydroxy reducing agent.

References Cited in the file of this patent UNITED STATES PATENTS 1,844,199 Bicknell et al. Feb. 9, 1932 2,663,654 Miller et al Dec. 22, 1953 2,910,377 Owen Oct. 27, 1959 

1. A NORMALLY STABLE HEAT-SENSITIVE COPY-SHEET SUITABLE FOR THE THERMOGRAPHIC REPONDUCTION OF DIFFERENTIALLY RADIATION-ABSORPTIVE GRAPHIC ORIGINALS AND INCLUDING A VISIBLY HEAT-SENSITIVE LAYER CAPABLE OF UNDERGOING PEDRMANENT VISIBLE CHANGE ON BRIEF CONTACT OF SAID COPY-SHEET WITH A METAL TEST BAR AT A TEMPERATURE WITHIN THE APPROXIMATE RANGE OF 70*C. TO 150*C. AND COMPRISING AN ORGANIC AMINE MOLYBDATE AND A REDUCING AGENT REACTIVE THEREWITH. 